1. Field of the Invention
The present invention relates to a method for etching a silicon compound film and a process for forming an article, utilizing the method, and more particularly to a method for etching a film of silicon oxide, silicon nitride or silicon carbide suitable for the preparation of semiconductor devices such as integrated circuits, etc., wiring circuit boards, and recording head heater substrates for use in the recording system for recording utilizing heat energy, and a process for forming an article, utilizing the method.
2. Related Background Art
In the field of articles such as semiconductor devices such as integrated circuits, etc., wiring circuit boards or recording head heater substrates, it is an ordinary practice to utilize a multilayer wiring technique in the preparation of smaller and more precise articles such as semiconductor devices, wiring circuit boards and heater substrates.
According to the multilayer wiring technique, a lower wiring and an upper wiring are usually provided, and in order to keep an electrical insulation between these wirings, an insulating layer is provided between these wirings.
Silicon oxide, typically SiO.sub.2, silicon nitride, typically Si.sub.3 N.sub.4 and silicon carbide, typically SiC, are widely used as an insulating layer or a protective layer between the upper wiring and the lower wiring. Above all, silicon compounds such as silicon oxide, silicon nitride, silicon carbide, etc. are suitable not only for the process for preparing the abovementioned articles, but also for a protective layer from the viewpoint of thermal and chemical stability and thus are widely utilized.
The layer of silicon compound as mentioned above is etched, when required, to make throughholes, etc. and in order to meet an increasing demand for etching with more precise and dense pattern, a most suitable dry etching method is now desired.
As etching gases for dry etching of films or silicon compounds such as silicon oxide (hereinafter referred to as SiO.sub.2), silicon nitride (hereinafter referred to as Si.sub.3 N.sub.4), or silicon carbide (hereinafter referred to as SiC), fluorohydrocarbon gases such as CF.sub.4 , CF.sub.4 +H.sub.2, C.sub.2 F.sub.6, C.sub.3 F.sub.8, CHF.sub.3, etc. are known. Above all, a mixed gas of CHF.sub.3 +C.sub.2 F.sub.6 has a higher etching rate and a wide range for selection ratio of positive resist and Si, and is most suitable for etching of a silicon compound film. Particularly for a SiO.sub.2 film, a good etching uniformity can be obtained in a gas flow rate ratio (CHF.sub.3 /C.sub.2 F.sub.6) ranging from 0.1 to 0.9. This condition is also applied to etching of other silicon compounds and widely utilized in the preparation of semiconductor devices. That is, when etching is carried out in an etching gas atmosphere, where C.sub.2 F.sub.6 is more than CHF.sub.3, a good etching uniformity can be obtained at a commercially satisfactory etching rate.
However, it has been found that, in the etching of a silicon compound film with a mixed gas of CHF.sub.3 +C.sub.2 F.sub.6 and containing more C.sub.2 F.sub.6, and in the case that the underlayer is Al or Al-containing alloy, e.g. Al-Si, Al-Si-Cu, etc., reaction products of Al deposit, for example, at contact holes, giving the following adverse effects on the devices:
(1) The deposited reaction products of Al weaken adhesion to an upper layer to be formed successively thereon, giving often defects to the semiconductor devices.
(2) In case of a multilayer film, the deposited reaction products of Al sometimes form unevenness in the film, giving defects to the semiconductor devices.
(3) The deposited reaction products of Al, for example aluminum fluoride, sometimes lower the insulation between the adjacent electrodes, generating an interelectrode leakage.
(4) When the mixed gas is used in the process for preparing a recording head heater substrate of such a type as to utilize heat energy to change a liquid state and eject the liquid by the state change, the deposited reaction products of Al on the heat-working surface of the heater substrate sometimes deteriorate the thermal uniformity of the heat-working surface, causing fluctuations in the generation of bubbles in the liquid to deteriorate the liquid ejection stability.
In case of etching a silicon compound film with a mixed gas of CHF.sub.3 and C.sub.2 F.sub.6 and containing more CHF.sub.3, it is possible to suppress formation of reaction products of Al such as aluminum fluoride, etc. in contrast to the case of C.sub.2 F.sub.6 -rich mixed gas. However, a polymerization film of CF.sub.2 monomers is more readily formed in that case, and another problem such as lowering of etching rate, etc. is sometimes encountered.
Thus, a commercially applicable new etching method capable of solving the foregoing problems has been desired for etching a silicon compound film with a mixed gas of CHF.sub.3 and C.sub.2 F.sub.6.